DE102009048384A1 - Miniaturized online trace analysis - Google Patents

Abstract

The invention relates to a method for producing a device for forming a liquid optical waveguide (2), comprising the steps: providing a substrate (1), which is preferably in the form of a circular disk and is particularly preferably a silicon wafer, applying an etching mask that contains a substrate to be etched, Defined at least partially curved, preferably spiral-shaped microchannel (2), and the action of an etching medium (14) at a uniform flow velocity, the etching medium (14) preferably flowing essentially in the direction of the microchannel (2) to be etched.

Description

The invention relates to a device and a method for the spectroscopic measurement of substances dissolved in liquids. The invention further relates to a method for producing such a device.

In environmental analysis, in particular in water analysis, the detection and measurement of substances dissolved in low concentrations in liquids plays a major role. For this purpose, various spectroscopic methods such as absorption, transmission, fluorescence and Raman are known. For this purpose, liquids are analyzed, for example, in cuvettes or cells which consist of optically transparent, light-conducting material, for example quartz glass. In order to reduce the detection limit of the substances to be detected, it is known to realize the longest possible light paths within the liquid in which the substance to be detected is dissolved. For this example, elongated cuvettes, capillaries or liquid optical waveguides are used in which the light losses occurring along the long path of light are reduced by a totally reflective inner or outer coating. In this case, the refractive index of the totally reflective coating must be smaller than the refractive index of the liquid, usually water, in the liquid optical waveguide. Water has a refractive index of n = 1.33. To form a liquid waveguide for aqueous solutions are therefore internal coatings of amorphous fluorinated polymers such as Teflon AF 1600 or Teflon AF 2400 with refractive indices of 1.29 and 1.31 or inorganic layer materials such as nano-porous silica films and silica with Refractive indices down to 1.18 or magnesium fluoride-magnesium oxide hydroxide mixed layers with refractive indices down to 1.09 in question. The refractive indices refer to the wavelength of the sodium D line.

Liquid optical waveguides with lengths in the range of several meters are typically used to realize the above-mentioned long light paths. This leads to considerable dimensions of the resulting detection apparatus, with the result that the intended detection measurements can often only be carried out in the laboratory, whereas a timely detection of such trace substances on site, for example directly on a water to be examined is desirable. Due to the dimensions of known devices, however, such on-site use is prevented or at least considerably more difficult.

Alternative measurement methods that do not require long optical paths, such as atomic absorption spectroscopy (AAS), the use of inductively coupled plasma mass spectrometry (ICPMS), and ion chromatography also require very large and costly devices.

The object of the present invention is to provide a miniaturized measuring device which nevertheless provides a long light path within the liquid to be examined, a production method for such a measuring device and a corresponding measuring method.

The invention is based on the finding that a liquid optical waveguide, contrary to the previously known embodiments, does not have to have a circular cross section, wherein the cross section is the area of the cavity to be filled with liquid, which results in a section perpendicular to the longitudinal direction of the liquid optical waveguide. In other words, a light pipe also takes place when the cross section of the liquid optical waveguide deviates from the known circular shape. Building on this knowledge, the idea underlying the present invention is not to provide the liquid optical waveguide as a self-supporting element, but rather as a closed microchannel on a suitable substrate. A self-supporting liquid optical waveguide in the context of the present specification is an elongate hollow body which is coated internally to form a liquid optical waveguide and consists of a material which is sufficiently stable mechanically, so that no further element for stabilization is necessary. Such a self-supporting liquid optical waveguide need only be supported at individual, spaced points.

Accordingly, the measuring device according to the invention comprises a device for forming a liquid optical waveguide. The latter comprises a substrate with an at least partially curved microchannel. The microchannel forms the liquid optical waveguide after appropriate lining with a low-refractive coating, after providing a suitable cover and after filling with liquid. Due to the at least partially curved formation of the microchannel, a correspondingly curved liquid optical waveguide is realized on the substrate. As a result, the length of the liquid optical waveguide is not limited by the outer dimensions of the substrate, as is the case with straight-line microchannels. Rather, the microchannel may be provided with a plurality of loops or windings on the substrate surface, for example, so that a long microchannel and thus a correspondingly long liquid optical waveguide can be realized even with small dimensions of the substrate.

Such a microchannel can in principle be provided with various methods in a substrate, for example by embossing polymers, such as polycarbonate, or milling. According to the invention, the microchannel is introduced into the substrate by etching, preferably wet-chemical etching. For this purpose, a suitable substrate is provided in a first step. Since the light pipe within the liquid optical waveguide to be created depends predominantly on the coating still to be applied and thus the substrate plays a subordinate role for the light pipe, in principle a large number of substrates are suitable for the apparatus according to the invention. In the liquid optical waveguide, however, high pressures occur during the filling with the liquid to be examined and optionally also during the measurement, which may be on the order of several bars. Therefore, it is preferable to provide a substrate having a correspondingly sufficient mechanical stability. Quartz glass, borosilicate glasses such as Pyrex glass, soda lime glass, various polycarbonates and particularly preferably silicon, for example a silicon wafer, are therefore suitable as materials for the substrate.

In a further step, an etching mask is applied to the substrate surface, for example lithographically, which defines the microchannel to be formed. In this case, the material of the etching mask is matched to the etching medium and the substrate. For etching a silicon substrate in an acidic environment, for example, nitride is suitable as a material for the etching mask

In a further step, the etching medium acts on the substrate at the locations predetermined by the etching mask. The etching medium is gaseous or liquid and flows at a uniform perturbation rate on the surface of the substrate to be etched during the etching step. In other words, the flow rate during the etching step remains constant over time at each point of the surface of the substrate, wherein different flow velocities can occur at different locations of the substrate. As a result, a high reproducibility of the etched microchannel is achieved. The manufacture of the microchannel according to the invention by means of etching has the advantage, in comparison with milled or embossed microchannels, that surfaces of high quality, that is smooth surfaces with low surface roughness, are created in the microchannel, whereby the light conduction in the liquid optical waveguide to be created is improved.

Preferably, the etch in the substrate is isotropic, that is, the etch rate is substantially the same in all spatial directions, and is independent, for example, from the crystal planes in a silicon wafer. As a result, because of the uniform flow velocity of the etching medium, advantageously a microchannel with a substantially semicircular cross-section can be created whose depth is equal to or only slightly smaller than half its width. In this case, the depth of the microchannel is the distance between the plane of the substrate surface and the lowest point of the microchannel at a cutting line which is perpendicular to the longitudinal direction of the microchannel. The depth is measured along the surface normal of the substrate surface. The width of the microchannel is the distance of the intersections of the inner walls of the microchannel with the substrate surface along a cut line that is perpendicular to the longitudinal direction of the microchannel. The width is measured in the plane of the substrate surface. The ratio between the width and the depth of the etched microchannel, that is to say the aspect ratio of the microchannel, can be influenced in a targeted manner by the flow velocity of the etching medium. Such a semicircular microchannel is on the one hand advantageous for the light pipe in the later liquid optical waveguide and on the other hand allows the realization of a simple axial coupling and uncoupling of light by means of an optical waveguide. The microchannel preferably has a depth in the range between 50 and 500 .mu.m, in particular 200, 250, 300, 400 or 500 .mu.m, wherein each of said individual values can represent a range limit of the specified range of values. With such dimensions of the microchannel, a laminar liquid flow can be realized to a good approximation in the later liquid optical waveguide, that is to say that disturbing turbulences in the liquid are avoided for the spectroscopic examination. Furthermore, because of the small channel cross-section, the microchannel also has a total low volume, even with a large channel length, as a result of which the minimum quantity of a sample liquid to be examined is small. The channel lengths are preferably more than 1, 2, 3, 5, 10, 15, 20, 25 or 30 meters.

Preferably, the etching medium flows substantially in the direction of the microchannel to be etched. As a result, a microchannel with a semicircular cross-section can be created, that is to say a microchannel whose width and depth are essentially identical.

If a silicon monocrystal, for example a silicon wafer, is used as the substrate, then this can in principle be etched with an acid medium as well as with an alkaline medium. When etching in an alkaline medium, however, the crystal structure plays an important role and the etching form is defined by excellent crystal faces ({111} etch stop faces). Thus, with an etching in an alkaline medium, an isotropic etching is not possible, as well as a sectionally curved course of the microchannel. In an acidic environment, however, the etching is largely independent of the crystal structure. Thus, an isotropic etching can be realized, which allows the formation of an at least substantially semicircular microchannel, and also the course of the at least partially curved microchannel on the substrate surface can be chosen arbitrarily, in particular independently of the crystal structure of the silicon crystal.

In a preferred embodiment of the production method according to the invention, the substrate to be etched is circular disk-shaped, as is the case, for example, with a silicon wafer. If, during the etching step, a stirring conical or disc-shaped stirring disc that is tapered on both sides is positioned and rotated centrally above the surface of the substrate to be etched, this can in a simple manner result in a laminar, uniform and homogeneous flow of the etching medium on the surface of the substrate to be etched will be realized. The flow velocity is preferably radially homogeneous, that is, in at least one given radial region on the substrate surface, the etching medium flows in the azimuthal direction, so that the flow velocity of the etching medium is identical at different radii. In other words, the rotational speed of the etching medium in the given radial range is indirectly proportional to the respective radius. In this context, centered means that the axis of rotation and symmetry of the stirring fish or of the stirring disk is a surface normal of the circular disc-shaped substrate and extends through the center of the circular disc-shaped substrate. Furthermore, the microchannel to be etched on such a circular disk-shaped substrate preferably extends substantially in the azimuthal direction with respect to the center of the circular disk-shaped substrate. As a result, with the stirring arrangement described above during the etching step, a laminar, uniform and radially homogeneous flow of the etching medium is generated, which essentially goes in the direction of the microchannel to be etched. The microchannel to be etched is preferably formed spirally, wherein the center of the spiral at least substantially coincides with the center of the circular disc. This is particularly preferably an Archimedes spiral, in which the radius of the spiral arm, that is to say of the microchannel, is proportional to the azimuthal angle.

For the purposes of the present specification, the term "helical" is understood to mean a shape which has at least one complete revolution about a center and whose radius around this center changes monotonically, preferably in proportion to the azimuthal angle. The preferred spiral formation of the microchannel has the advantage that a large number of closely adjacent turns can be provided on the substrate surface. Preferably, adjacent turns have a distance from one another, between 800 and 1500 μm, preferably 800, 900, 1000, 1200 or 1500 μm. Thus, a large surface portion of the substrate surface for the formation of the microchannel can be provided, whereby a large length of the microchannel and a correspondingly long light path can be realized in the liquid optical waveguide to be created. In addition, the curvature of the microchannel, that is the change in the longitudinal direction along the longitudinal direction, changes continuously and monotonically, preferably linearly, maximizing the radius of curvature at each point of the microchannel, avoiding small radii of curvature and thus the flow resistance for the liquid within the mold Liquid optical waveguide is minimized. The monotonous course of the curvature of the microchannel and of the corresponding liquid optical waveguide furthermore has the decisive advantage that only a minimal number of loss modes occurs in the light pipe, and thus the optical conductivity of the liquid optical waveguide to be formed is maximized. Preferably, the minimum radius of curvature of the optionally spiral-shaped microchannel is 20 mm, 10 mm or 5 mm.

In a preferred embodiment of the production method according to the invention for the microchannel, the action of the etching medium takes place in several steps. In between, the etching is interrupted and the substrate with the applied etching mask is rinsed with a suitable substance, for example with water. Such a stepwise etching has the advantage that the etch mask has a higher resistance during the etching and thus a micro channel of high quality and depth can be created. Preferably, for each etching step, a fresh, completely unused, optionally newly prepared etching medium is used.

After etching, the etching mask is removed. Before closing the microchannel, the inner wall of the microchannel can be smoothed by polishing it with gaseous hydrofluoric acid and gaseous ozone.

Subsequently, the etched and possibly polished microchannel is closed. For this purpose, in a first preferred embodiment of the method, the etched microchannel is covered with a planar cover plate. Subsequently, the cover plate is mounted on the substrate and thereby the etched micro-channel closed and thus formed a closed micro-channel. The materials of substrate and cover plate may be identical or different. For example, can a planar cover plate made of quartz glass on a substrate made of silicon, for example, be mounted on a silicon wafer by anodic bonding. Alternatively, the cover plate itself may be made of silicon and, for example, be another silicon wafer, which is attached by means of silicon-silicon direct bonding (SDR) on the etched silicon wafer. Other materials and combinations of materials may also be mechanically bonded by bonding or other bonding processes. Alternatively, all attachment methods are suitable that provide a sufficiently mechanically stable connection between the substrate and cover plate and thereby provide sufficient fluid and light tightness of the closed microchannel. In the case of anodic bonding, the substrate and cover plate are brought to a high temperature, for example 500 ° C., and a high voltage, for example 1 kV, is applied between substrate and cover plate.

In a further step, the closed channel is provided with a low-refractive coating. The coating preferably consists of Teflon, nanoporous silicon dioxide or a nanoporous double compound of magnesium fluoride-magnesium oxide hydroxide. The coating material is dissolved in a suitable solvent, for example FC40, FC75 or FC77, and the solution injected into the closed microchannel. For this purpose, for example, a suitably shaped cannula is introduced into the closed microchannel, which distributes the solution with the coating material to be applied in the closed microchannel. Subsequently, the closed microchannel is purged with gaseous nitrogen.

Thereby, a closed, coated microchannel is created, which is hollow inside and, when filled with a suitable liquid having a higher refractive index than the low refractive coating, for example water, a liquid optical waveguide is formed. The closed microchannel is completely lined with the low refractive coating.

In an alternative embodiment of the method for creating a closed, coated microchannel, the substrate surface is provided with the etched microchannel and the surface of the planar cover plate with a low-refractive coating prior to joining substrate and cover plate. The coating preferably consists of Teflon, nanoporous silicon dioxide or a nanoporous double compound of magnesium fluoride-magnesium oxide hydroxide. For this purpose, a solution with the coating material to be applied, for example by spin coating or spray coating, is applied to the substrate surface with the etched microchannel and the surface of the planar cover plate. Spin coating, also called spin coating, is a process for applying thin and uniform layers or films on a substrate. It is suitable for applying in principle all materials present in solution. The substrate, for example, a silicon wafer is fixed on a turntable and rotated at a certain speed and for a certain time. With a metering device over the center of the rotating substrate, a desired amount of the solution is applied, wherein the solution is evenly distributed over the substrate surface and centrifuged excess solution. Preferably, the solution is applied in several steps and the substrate is heated between these steps, so that the solvent evaporates and forms the optionally nanoporous structure of the coating. In spray coating, a fine mist of a solvent with coating material dissolved therein is produced and deposited on the substrate surface with the etched microchannel and the surface of the planar cover plate. After evaporation of the solvent, the coating material previously dissolved in the solvent remains on the surface. Preferably, the spray coating also takes place in several steps, for example in four steps, between which the substrate is rotated by 90 ° and heated.

Subsequently, the substrate is covered with the planar cover plate, so that the respective low-refractive coatings of the substrate surface and the planar cover plate come to rest on each other. Substrate and cover plate are then glued together by heating substrate and cover plate. However, the substrate and the cover plate, in particular when using Teflon as coating material, are not heated above the glass transition temperature above the destruction temperature of the coating material. As a result, the two low-refractive coatings combine to form a closed microchannel that is completely lined with a low-refractive coating.

The low-refractive coating of the device according to the invention for forming a liquid optical waveguide has a thickness of 2 to 10 .mu.m, in particular 2, 3, 4, 5 or 10 .mu.m, wherein said individual values can represent range limits of said range of values.

In a preferred embodiment of the device according to the invention for forming a liquid optical waveguide, a feed line is formed in the substrate, which feeds in and out of liquid into the closed microchannel and out of the closed microchannel allowed. Preferably, a supply line is formed at both ends of the microchannel, one of which supplies the liquid to the closed microchannel and the other discharges the liquid from the closed microchannel. Thus, the liquid in the liquid optical waveguide can be easily exchanged and, in particular, a continuous liquid flow can also be provided during the spectroscopic measurement. It is advantageous if there is a laminar flow within the liquid optical waveguide and disturbing turbulence in the liquid is avoided for the spectroscopic examination. This is inventively achieved in that the leads extend non-axially with respect to the longitudinal directions of the microchannel and preferably form an angle between 10 and 90 degrees with the longitudinal direction of the microchannel at the point of intersection between feed line and microchannel, preferably 10, 15, 20, 30, 45, 60 or 90 degrees. The individual values mentioned may be range limits of the stated value range.

Preferably, on the substrate at at least one end of the closed microchannel, preferably at both ends of the closed microchannel, a device is provided for the axial coupling and / or decoupling of light into the closed microchannel or out of the closed microchannel. Preferably, the device for axial coupling and uncoupling is designed as a receptacle for an optical waveguide, wherein the receptacle forms an axial, rectilinear continuation of the microchannel in the substrate. Due to the semicircular cross-section of the microchannel, such an optical waveguide, in particular a single-mode optical waveguide, can be suitably positioned in the microchannel, in particular if the diameter of the optical waveguide is equal to the depth of the microchannel. Particularly preferably, an element is provided in the microchannel between the liquid micro waveguide provided as a closed, closed microchannel and the optical waveguide, which ensures an effective on and / or off coupling of light. This microlens, in particular a GRIN lens (gradient index), is preferred.

Alternatively, the device for the axial coupling and / or decoupling of light into the closed microchannel can be designed as a deflection unit which deflects light from the direction of the cover plate axially into the closed microchannel and / or light out of the closed microchannel in the direction of the cover plate. This allows a coupling and / or decoupling of light in the closed microchannel even without optical fibers. In this case, the cover plate on suitable recesses or is translucent, which can be achieved for example by a cover plate made of quartz glass. The deflection unit can be, for example, a micromirror arranged in the substrate.

A translucent, transparent cover plate, for example made of quartz glass, has the advantage that the closed microchannel can thereby also be transversely penetrated. This is advantageous, for example, for fluorescence and Raman measurements, as explained in more detail below.

In a preferred embodiment of the device for forming a liquid optical waveguide, a micromixer and / or a micropump is formed on the at least one liquid feed line of the substrate. As a result, the device and also the resulting measuring device can be further miniaturized on the one hand. On the other hand, the provision of a micromixer allows the supply of two different liquids, whereby the degree of freedom in the design of the measuring method increases.

In addition to the described apparatus for forming a liquid optical waveguide, the measuring device according to the invention comprises a light source, a light detector and a first liquid pump, which supplies a sample liquid to the closed microchannel via the at least one feed line. The filled with the sample liquid, closed microchannel forms a liquid optical waveguide. The substance to be detected by spectroscopy is in dissolved form in the sample liquid. The sample liquid is preferably an aqueous solution, that is, the refractive index of the sample liquid substantially corresponds to the refractive index of water. The light source is set up to irradiate the closed microchannel with light.

In a first embodiment of the measuring device according to the invention, this is set up to carry out transmission or absorption measurements. For this purpose, the light of the light source is coupled axially into the closed microchannel or the liquid optical waveguide. This can be done via an optical fiber. In this case, the cover plate may be opaque and, for example, also be a silicon wafer. Alternatively, the axial coupling of the light of the light source can also be realized by the deflection unit described above, in which case the cover plate has suitable recesses and / or is translucent. In an analogous manner, the transmitted light at the other end of the microchannel is fed to the light detector, which in turn can be done with the aid of an optical waveguide or a suitable deflection unit.

Depending on the chosen measuring method, the light of the light source is monochromatic or broadband and lies in the UV and / or visible (VIS) wavelength range. Likewise, the transmitted light can be completely supplied to the light detector, or it can be spectrally filtered or split, for example via wavelength filters or a spectrometric unit. In broadband irradiation of light and subsequent spectral splitting of the transmitted light this different light detectors can be supplied, whereby at the same time several measurements at different wavelengths can be performed in parallel and thus different solutes can be measured simultaneously.

In a particularly preferred embodiment, the light source emits monochromatic light in the visible wavelength range and the light detector detects the entire transmitted light without prior spectral filtering. In a further preferred embodiment, the coupling and decoupling via the above-mentioned deflection units, whereby the light source and the light detector can be arranged directly on the substrate or the cover plate of the apparatus for forming a liquid optical waveguide. Particularly suitable for such an embodiment are LED diodes or semiconductor laser diodes as a light source and photodiodes, for example avalanche photodiodes as a light detector, which are available as components with small external dimensions. As a result, the measuring device according to the invention is further miniaturized. Avalanche photodiodes, also called avalanche photodiodes, are high-sensitivity and fast photodiodes that use the avalanche breakdown (avalanche effect) that is also used in zener diodes.

In a further preferred embodiment, the cover plate of the device for forming a liquid optical waveguide is translucent and preferably made of quartz glass and particularly preferably provided with a for the irradiated light, for example for UV light, anti-reflective coating. Thus, light of the light source, which is preferably an excitation light source, transversely, that is perpendicular to the longitudinal direction of the microchannel, are irradiated through the cover plate, wherein by the total or Fresnell reflection on the coated channel walls light with high yield in the liquid optical waveguide is coupled. This arrangement is suitable for fluorescence and Raman measurements wherein the fluorescent light generated in the sample liquid is collected by the liquid optical waveguide and directed to the ends of the liquid optical waveguide. In this embodiment, preferably UV light is irradiated and the fluorescent light is coupled out axially and fed to the light detector after optionally spectral filtering. In this case, a spectral filtering of the excitation light and thus a corresponding filter element can be dispensed with, since the transversely irradiated excitation light has a large angle of incidence on the coating of the microchannel, so that no total reflection takes place. Accordingly, the excitation light is also not passed through the liquid optical waveguide to the light detector.

With the measuring device according to the invention and the measuring method according to the invention, a wide variety of substances can be detected on the basis of characteristic absorption bands during transmission and absorption measurements. Depending on the substance to be detected, the light of the light source as well as a possible spectral filtering of the incident light is selected. For example, organic solvents such as acetone, benzopyrene, benzene or anions such as nitrate or phosphate can be detected, which have characteristic absorption bands in the near UV range. Similarly, conjugated π-system organic compounds can be detected, which typically have absorption bands in the visible wavelength range. Likewise, Ni ^{2+ has} a characteristic absorption band at 670 nm.

In the measuring device according to the invention, the liquid pump which supplies the sample liquid to the closed microchannel is preferably integrated on the substrate of the device for forming a liquid optical waveguide as a micropump. As a result, the measuring device according to the invention can be further miniaturized.

In a further preferred embodiment of the measuring device, this is designed to supply the closed microchannel in addition to the pump liquid and a second detection liquid. These two liquids are mixed prior to introduction into the closed microchannel, which preferably occurs via a micromixer integrated in the substrate of the apparatus for forming a liquid optical waveguide. The detection fluid is supplied to the micromixer via a further fluid pump, wherein the mixing ratio of sample fluid and detection fluid can be adjusted via the two fluid pumps. Preferably, both liquid pumps are integrated as micropumps on the substrate of the device for forming a liquid optical waveguide, which further miniaturizes the measuring device according to the invention.

In a particularly preferred embodiment of the measuring method according to the invention, metal ions are detected. A direct observation of such metal ions by means of Absorbance measurement is generally not possible because metal ions typically have low UV absorption bands. In a preferred embodiment of the measuring method according to the invention, these metal ions trigger a detection reaction, wherein the product of the detection reaction can be detected by means of an absorption measurement. For this purpose, in addition to the sample liquid containing the metal ions to be detected, the closed microchannel is also supplied with a detection liquid in which a suitable complexing agent is dissolved. When mixing the samples and the detection liquid in the micromixer, the metal ions enter into coordination compounds with the complexing agent, the resulting metal complexes having allowed charge-transfer transitions with large extinction coefficients ε, which have a strong absorption in the visible wavelength range. In this case, the detection of metal ions can be done advantageously via the absorption of monochromatic visible light. A further spectral filtering in front of the light detector is advantageously not necessary.

In a first preferred embodiment of the measuring method, Cu ²⁺ ions are detected and used as complexing agent 1,10-phenanthroline (C ₁₂ H ₈ N ₂ ). The resulting metal complex has an absorption at 650 nm. In a further preferred embodiment, Fe ²⁺ ions are detected, which form a metal complex with 1,10-phenanthroline as a complexing agent, which has an absorption at 510 nm. Likewise, Fe ²⁺ ions can be reacted with 3- (2-pyridyl) -5,6-bis (4-phenylsulfonic acid) -1,2,4-triazine-5 ', 5 "-disodium salt (C ₁₆ H ₈ N ₄ Na ₂ O ₈ S ₂ ) can be detected as a complexing agent, the resulting complex showing an absorption at 567 nm.

Further exemplary embodiments and advantages of the invention are explained below by way of example with reference to the accompanying figures. The examples represent preferred embodiments which in no way limit the invention. The figures shown are schematic representations that do not reflect the real proportions, but serve an improved clarity of the various embodiments.

In detail, the figures show:

1 a schematic view of the measuring device;

2 a plan view of a spiral-shaped liquid optical waveguide;

3 a cross-section through a first embodiment of a coated, closed microchannel;

4 a cross-section through a second embodiment of a coated, closed microchannel;

5 a longitudinal section through a measuring device for fluorescence measurement;

6 an arrangement for etching a silicon substrate;

7 a first embodiment of a micromixer; and

8th A second embodiment of a micromixer.

In 1 an embodiment of a measuring device is shown schematically. It is on a circular wafer silicon wafer 1 a spiral microchannel 2 educated. The microchannel is coated in the embodiment with Teflon and forms when supplying an aqueous solution, a liquid optical waveguide 2 out. Alternatively, the microchannel may be coated with a nanoporous silica or magnesium fluoride magnesium oxide hydroxide. The microchannel 2 is with one in the 1 Not shown cover plate covered, so that there is a hermetically sealed microchannel, which is light and liquid-tight. The measuring device further comprises a monochromatic light source 4 , a light detector 5 and optical fibers 3 which allow axial coupling and uncoupling of light in the closed microchannel. As a result, on the one hand, the monochromatic visible light of the light source 4 be coupled axially into the liquid optical waveguide and on the other hand, the transmitted light axially from the liquid optical waveguide 2 be disconnected and the light detector 5 be supplied. This allows absorption and transmission measurements in the liquid optical waveguide 2 make. The light detector used is an avalanche diode. Alternatively, other types of photodiodes or other suitable light detectors may be used. In particular, it is also possible to provide spectral filtering upstream of the light detection (by means of a wavelength filter or by means of spectrometric methods). If the miniaturization requirements are less stringent, it is also possible to use larger-sized light sources and / or light detectors, which can be used with the liquid-optical waveguide via, for example, self-supporting optical waveguides 3 visually connected. Between the liquid fiber optic cable 2 and the optical fibers 3 are not shown Microlenses, such as GRIN lenses (Gradient Index), provided in order to increase the yield of the coupled and outcoupled light with a small aperture.

The liquid optical waveguide is via leads 6 . 6a . 6b Liquid supplied and discharged. This is a sample liquid 7 and a detection fluid 8th each via micropumps 9 in the supply line 6 pumped. sample liquid 7 and detection fluid 8th be in the micromixer 10 before supplying to the liquid optical waveguide 2 mixed in a predetermined mixing ratio, wherein micromixer 10 and micropumps 9 in 1 separated from the silicon wafer 1 are shown. In an alternative embodiment, the micropumps are 9 , the micromixer 10 and the corresponding supply lines 6 . 6a . 6b however, on the silicon wafer 1 integrated, resulting in a considerable miniaturization of the entire measuring device. In the measuring device, the spectroscopic absorption and transmission measurements in the liquid optical waveguide 2 be made dormant or flowing liquid. The discharged liquid is in a collection container 11 collected and can then be discarded.

In the in 1 the measuring device shown, it is possible to mix two liquids before the supply line to the liquid optical waveguide in a predetermined mixing ratio. Thus, for example, metal ions in the sample liquid 7 be detected. These metal ions often have absorption bands in the deep UV range, which is not easily accessible to absorption and transmission measurements. An exception to this is, for example, the Ni ²⁺ ion, which shows in aqueous solution an absorption at 670 nm, which can be used to detect such Ni ²⁺ ions. The sample liquid 7 with the metal ions dissolved in aqueous solution is mixed with the detection liquid 8th in which a suitable complexing agent is dissolved in likewise aqueous solution. The complexing agent forms a coordination compound with the metal ion, the resulting complex having allowed charge-transfer transitions having a high extinction coefficient (ε> 1000) and being in the visible spectral range. For example, Cu ²⁺ ions with the complexing agent 1,10-phenanthroline (C ₁₂ H ₈ N ₂ ) form an ionic complex with a copper ion and three 1,10-phenanthroline molecules ([Cu (C ₁₂ H ₈ N ₂ ) 3 ] ²⁺ ), which has a characteristic absorption band at 650 nm. The same complexing agent can also be used to detect Fe ²⁺ ions, which together with 1,10-phenanthroline form an ionic complex of one Fe ion and three 1,10-phenanthroline molecules ([Fe (C ₁₂ H ₈ N ₂ ) ₃ ] ²⁺ ), which has a characteristic absorption band at 510 nm. Fe ²⁺ ions can also be combined with the anion of the 3- (2-pyridyl) -5,6-bis (4-phenylsulfonic acid) -1,2,4-triazine-5 ', 5 "-disodium salt [C ₁₆ H ₈ N ₄ O ₈ S ₂ ] ^{2- form} a complex ([Fe (C ₁₆ H ₈ N ₄ O ₈ S ₂ ) 3] ^4- ), which has a characteristic absorption at 567 nm.

The use of complexes for detecting metal ions has the advantage that the characteristic absorption of the complex formed is in the visible spectral range. As a result, light-emitting diodes (LED) or semiconductor lasers can be used as light source, which are available as inexpensive components with small dimensions and can deliver monochromatic light in the visible wavelength range. The monochromatic light is typically sufficiently narrow band that all the light without prior spectral filtering can be used for the absorption measurement and can be detected by a light detector without further spectral filtering. As a result, it is possible to use components with small external dimensions both as a light source and as a light detector, which can advantageously be arranged directly on the silicon wafer or on an overlying cover plate. This makes it possible in total to integrate a variety of necessary for the supply of liquids and light devices on the substrate and thus to miniaturize the measuring device significantly.

The use of complex images to detect metal ions has the advantage of providing characteristic absorption bands in the visible spectral range. Above all, their extinction is significantly greater than the extinction of the metal ions themselves. Thus, the detection limit for metal ions can be significantly reduced. Also by the large channel length of the microchannel 2 and the resulting long light path in the liquid optical waveguide 2 the detection limit can be significantly reduced. Overall, measurements in the sub-ppb range are possible.

This in 1 illustrated embodiment allows a miniaturized structure of a measuring device, which nevertheless provides large optical path lengths and thus enables low detection limits. The additional use of suitable detection reactions further reduces the detection limit.

In the in 1 As illustrated embodiment, a 4-inch silicon wafer is used as a substrate in which a microchannel is etched with a depth of 250 microns. The microchannel is covered with a translucent, planar cover plate made of quartz glass, not shown. The microchannel is coated with a 3 μm thick coating of Teflon, so that the closed and coated microchannel 2 a liquid optical waveguide 2 forms for aqueous solutions.

In 2 is the silicon wafer 1 shown in greater detail. The spiral-shaped microchannel 2 is formed apart from the end portions as Archimedes spiral, that is, the radius r of the microchannel 2 changes starting from the midpoint 18 (Center of symmetry) of the spiral linearly with the azimuthal angle φ of the spiral. The spiral has a pitch of 600 μm. The pitch is the change in the radius r of the spiral microchannel 2 after passing through an azimuthal angle φ of 2π. This ensures a large overall length of the microchannel and the corresponding liquid optical waveguide. In the illustrated embodiment, the length of the liquid optical waveguide is about 4.7 meters.

How out 2 seen, the microchannel 2 not to the center 18 the spiral continues, as with increasing radius of curvature of such a liquid optical waveguide increased light losses occur because the angle of incidence of light on the interface between the liquid core of the liquid optical waveguide and the low-refractive coating becomes larger and thus the condition of total reflection of a smaller proportion of the light is maintained , In other words, the proportion of the modes of loss of light in the liquid optical waveguide decreases 2 to. Therefore, in the in 2 illustrated embodiment on the 4-inch silicon wafer disk, the spiral of the microchannel 2 only up to a minimum spiral radius of 1 cm. Thereafter, the light from the liquid optical waveguide 2 decoupled. Loss of light due to the radius of curvature of the liquid optical waveguide can be reduced by using the low refractive, totally reflective coating in the microchannel 2 on a highly reflective substrate 1 is applied. Such a highly reflective surface can be obtained using silicon as the substrate, since silicon is metallically reflective. Furthermore, it is advantageous in this case if the microchannel has a smooth surface, as is achieved, for example, during etching, in particular during wet-chemical etching of such a silicon substrate. Alternatively, the light losses at small radii of curvature can also be reduced if a totally reflecting coating with a particularly low refractive index is used. This can be achieved by the use of nanoporous silica or magnesium fluoride-magnesium oxide hydroxide.

As in 2 schematically illustrated, light is transmitted via waveguides, for example 3 axially coupled into and out of the liquid optical waveguide. Furthermore, liquid is supplied via supply lines 6 supplied to the liquid optical waveguide and removed therefrom. As in 2 can be seen, show the supply lines 6 an angle of 30 ° with respect to the longitudinal axis of the microchannel 2 , This ensures a laminar flow within the liquid optical waveguide. Alternatively, depending on the selected hydraulic conditions within the liquid optical waveguide, other angles between the feed line and the longitudinal axis of the liquid optical waveguide can be selected.

In the 3 and 4 is a cross section through the microchannel 2 shown. In both figures, the microchannel is through a transparent cover plate 12 made of, for example, quartz glass hermetically closed. Furthermore, the microchannel 2 completely lined with a totally reflective, low-refractive layer. The in 3 shown closed microchannel was made by the fact that the quartz glass cover plate 12 on the silicon substrate 1 attached by anodic bonding. Subsequently, Teflon was injected into the closed microchannel and purged with gaseous nitrogen, leaving the closed microchannel 2 completely from a totally reflective Teflon coating 13 is enclosed with a layer thickness of 3 microns. Anodic bonding provides a closed microchannel that is sufficiently liquid and light-tight to form a liquid optical waveguide.

The in 4 The closed and coated microchannel shown was fabricated using an alternative manufacturing process. At first, the quartz glass cover plate was used 12 and the etched silicon substrate 1 coated with Teflon by spin-coating or spray-coating method. Subsequently, the substrate became 1 and the cover plate 12 with the coated sides laid on each other and the entire assembly heated to a temperature of 330 ° C. As a result, the Teflon coatings of substrate stick together 1 and cover plate 12 next to the etched microchannel 2 and in sum there is also a closed microchannel 2 that of a totally reflective layer 13 is completely surrounded and sufficiently liquid and light-tight to form a liquid optical waveguide.

In 5 is a longitudinal section through a measuring device for fluorescence measurements shown. In this case, excitation light, for example UV light, (coming from above in the figure) through a quartz glass cover plate 12 transversally into the liquid optical waveguide 2 coupled. In the in the liquid optical waveguide 2 contained liquid, fluorescent light is generated at the low-refractive layer 13 totally reflected and to the ends of the liquid optical waveguide 2 is directed. The cover plate 12 is with a UV-reflective anti-reflective coating 17 to minimize losses due to reflection during transversal coupling of the excitation light. to Increasing the yield of fluorescent light of the substance to be detected, the substance can be marked in advance with fluorescent dyes and then measured. The illustrated measuring device may alternatively be used for Raman measurements in which the excitation light is typically in the visible spectral range. The anti-reflective coating 17 then acts in the visible spectral region anti-reflective.

In 6 is an embodiment of an apparatus construction for the etching of a silicon substrate 1 shown schematically. This is a circular disk-shaped silicon wafer 1 with a diameter of four inches of an etching solution 14 exposed. The etching takes place in an acidic medium and the etching solution contains acids such as hydrofluoric acid, acetic acid, nitric acid and / or hydrogen peroxide in suitable proportions, optionally with surfactant. In this liquid etching solution 14 becomes the silicon wafer to be etched 1 attached to the process side up in a suitable Ätzbehälter. The bottom side of the silicon wafer 1 is passivated. The illustrated arrangement of the process side of the silicon wafer 1 Upwards has the advantage that possibly occurring gases can easily escape during the etching. Two centimeters above the circular wafer silicon wafer 1 becomes a rotationally symmetrical agitator 15 with a conical stirrer or a disc-shaped stirrer disc 19 centrally positioned and rotated. As a result, a laminar flow flow is realized within the etching solution, resulting in a uniform, homogeneous flow rate of the etching medium on the wafer surface. Such a laminar, homogeneous flow optimizes the etching rate since used etching solution is continuously removed at every point of the wafer surface. The etching temperature should be in the diffusional-controlled area. Accordingly, the etch rates in the vertical direction, that is, perpendicular to the wafer surface, and horizontal direction, that is, along the wafer surface, are substantially the same, thereby, to a good approximation, an isotropic etch and a microchannel 2 achieved with corresponding semicircular cross section. Such a semicircular cross section is in the 3 and 4 Furthermore, the laminar, uniform flow at the process surface of the silicon wafer ensures a round and smooth etched trench and thus a microchannel 2 with smooth surface and low surface roughness.

For additional smoothing of the surface of the microchannel, if required, the microchannel can be processed with a gas mixture of hydrofluoric acid and ozone. The gas is distributed over a nozzle array evenly over the entire wafer. This resulting polishing removal is 1-2 μm.

In the illustrated embodiment, the etching of the microchannel occurs 2 in several steps. For example, each etching step lasts 4 Minutes. Subsequently, the silicon wafer 1 from the etching solution 14 removed and rinsed with water. Subsequently, the silicon wafer is returned to the etching solution 14 used, by means of the agitator 15 again a laminar flow of the etching solution 14 generated and carried out a further etching step with a predetermined duration and fresh, newly prepared etching solution, for example, again 4 minutes. By such a sequential etching in several etching steps, which are interrupted by rinsing of the silicon wafer, the durability of the etching mask, which consists in the embodiment of nitride, is improved. Thus, an uncontrolled expansion is largely avoided and it is obtained a micro-channel with high quality.

In 7 is a micromixer shown on the silicon wafer 1 is integrated. The micromixer 10 It allows two liquids, each over the supply lines 6a and 6b to flow, to mix effectively and these over supply lines 6 the liquid optical waveguide 2 supply. The supply lines 6a and 6b can be dimensioned according to the planned application, are in 7 but shown with identical diameter. Since there are generally no turbulences in microchannels, it would be easy to merge the leads 6a and 6b to a common supply line 6 to no flow-related mixing of the two liquids (sample liquid 7 and detection fluid 8th ) come.

In the in 7 Micromixers shown form the ends of the leads 6a and 6b the input channels of the micromixer 10 and the beginning of the supply line 6 the output channel of the micromixer 10 , In 7 the input channels and the output channel are arranged in parallel. Alternatively, however, they can also be arranged at an angle to one another. The two input channels and the output channel are each via a plurality of parallel flow channels 16 connected, which are arranged non-perpendicular to the input channels and the output channel. Neighboring river channels 16 are each by slats 20 separated from each other. The flow channels have a length between 100 and 1000 microns and a width between 20 and 500 microns.

The micromixer does not necessarily have a symmetrical structure. Rather, it can be optimized for the intended application and on both sides, that is in the part of the supply of the sample liquid 7 serves and in the part of the supply of the detection fluid 8th serves to be differently structured. In particular, different lengths and / or different widths of the parallel flow channels can be provided on both sides.

In the in 7 illustrated embodiment, the lengths of the flow channels are identical on both sides and each amount to 1000 microns. On the in 7 On the left side, the supply of the detection fluid 8th over the supply line 6b serves, the flow channels have a width of 50 microns. On the in 7 Right side, which is the supply of sample liquid 7 over the supply line 6a serves, have the river channels 16 a width of 500 microns. With the same width of the flow channels 16 separating slats 20 of 100 microns, has in the illustrated embodiment, the right side (sample liquid 7 ) of the micromixer 10 in the region between the input channel and the central output channel, a smaller number of flow channels 16 , a correspondingly smaller number of slats 20 and thus an overall higher flow cross section than the corresponding left side (detection liquid 8th ) of the micromixer. Thus, the favored in 7 illustrated micromixer 10 a mixing ratio of the resulting liquid mixture with a larger proportion of sample liquid 7 and a smaller proportion of detection fluid 8th , The mixing ratio continues to be through that in the supply lines 6a and 6b affected pumps.

In the in 8th illustrated second embodiment of the micromixer 10 Both sides of the micromixer have the same structure. The length of the river channels 16 here is 200 microns and the width of the flow channels 16 is 50 μm. The width of the slats is 20 μm and the length of the slats is equal to the length of the flow channels. Furthermore, the river channels 16 on the left and right sides of the micromixer 10 arranged offset to each other, so that the ends of the flow channels 16 in each case opposite the end face of a lamella. By this construction of the micromixer 10 In the output channel, small-sized layer stacks of the two liquids to be mixed are produced, which rapidly mix via diffusion. This effect also occurs in the 7 shown first embodiment of the micromixer 10 on.

The in the 7 and 8th micromixers thus ensure an effective mixing of two different liquids to use without turbulence.

Claims (15)

Method for producing a device for forming a liquid optical waveguide ( 2 ), comprising the steps of: - providing a substrate ( 1 ), which is preferably circular disk-shaped and particularly preferably is a silicon wafer, - application of an etching mask which comprises a microchannel to be etched, at least partially curved, preferably spiral-shaped ( 2 ), and - acting on an etching medium ( 14 ) at a uniform flow rate, wherein the etching medium ( 14 ), preferably substantially in the direction of the microchannel to be etched ( 2 ) flows. Method according to claim 1, characterized in that the action of the etching medium ( 14 ) takes place in several steps and in each case the substrate is preferably rinsed with water in each case and for each etching step an unconsumed etching medium ( 14 ) is used. Method according to claim 1 or 2, comprising the further steps of: covering the etched microchannel ( 2 ) with a cover plate ( 12 ), - fastened the cover plate ( 12 ) on the substrate ( 1 ) for forming a closed microchannel ( 2 ), preferably by a bonding process, particularly preferably by anodic bonding, and - application of a low-refractive coating ( 13 ), preferably from Teflon, nanoporous silica or a nanoporous double compound of magnesium fluoride-magnesium oxide hydroxide, to the inside of the closed microchannel by injecting a solution containing the coating material into the microchannel and purging the microchannel with nitrogen. Method according to claim 1 or 2, comprising the further steps of: applying a low-refractive coating, preferably of teflon, nanoporous silica or a nanoporous double compound of magnesium fluoride-magnesium oxide hydroxide, to the etched substrate surface and the surface of a cover plate ( 13 ) by spin-coating or spray-coating, - covering the substrate ( 1 ) with the cover plate ( 13 ), so that the respective low-refractive coatings ( 13 ), and - bonding of substrate ( 1 ) and cover plate ( 12 ) by heating to form a closed microchannel ( 2 ). Apparatus for forming a liquid optical waveguide comprising a substrate ( 1 ) with an at least partially curved, preferably spiral-shaped microchannel ( 2 ) coated with a low refractive index coating ( 13 ) and with a cover plate ( 12 ) for forming a closed microchannel ( 2 ) is covered, the cover plate ( 12 ) at least above the microchannel ( 2 ) with another low-refractive coating ( 13 ) is provided. Device according to claim 5, characterized in that in the substrate ( 1 ) at least one supply line ( 6 ), which is a supply of liquid in the closed microchannel ( 2 ) and / or a discharge of liquid from the closed microchannel ( 2 ), preferably at the ends of the microchannel ( 2 ) each a supply line ( 6 ) is trained. Apparatus according to claim 5 or 6, characterized in that at least at one end of the closed microchannel ( 2 ), preferably at both ends of the microchannel ( 2 ), a device for the axial coupling of light into the closed microchannel and / or for the axial outcoupling of light from the closed microchannel (US Pat. 2 ) is provided. Apparatus according to claim 7, characterized in that the device for axial input and / or decoupling of light as a receptacle for an optical waveguide ( 6 ) is formed, the one input and / or decoupling via the optical waveguide ( 6 Preferably, the receptacle is provided as an axial, rectilinear continuation of the microchannel in the substrate (FIG. 1 ) is trained. Device according to one of claims 5 to 8, characterized in that the cover plate ( 12 ) is translucent, preferably made of quartz glass, and particularly preferably with an anti-reflective coating in the UV and VIS spectral range ( 17 ) is provided. Device according to one of claims 6 to 9, characterized in that in the at least one supply line ( 6 ) a micromixer ( 10 ) and / or a micropump ( 9 ) is trained. Measuring device comprising a device according to one of claims 7 to 10, and a light source ( 4 ), which is set up, the closed microchannel ( 2 ) with light, a light detector ( 5 ), a first liquid pump ( 9 ), the closed microchannel ( 2 ) via the at least one supply line ( 6 . 6a ) a sample liquid ( 7 ) feeds. Measuring device according to claim 11, further comprising: a second fluid pump ( 9 ), the closed microchannel ( 2 ) via a micromixer ( 10 ) a detection liquid ( 8th ) feeds. Measuring device according to claim 11 or 12, further comprising: a first optical waveguide ( 3 ) arranged at a first end of the closed microchannel ( 2 ) Light of the light source ( 4 ) in the closed microchannel ( 2 ) axially, wherein the light source ( 4 ) is preferably set up to emit monochromatic, visible light and / or a second optical waveguide ( 3 ) established at a second end of the closed microchannel ( 2 ) Light from the closed microchannel ( 2 ) and the light detector ( 11 ). Measuring method for a measuring device according to one of claims 11 to 13, comprising the steps: - supplying sample liquid ( 7 ) and preferably detection fluid ( 8th ) in the closed microchannel ( 2 ), - axial coupling of light of the light source ( 4 ) in the closed microchannel ( 2 ) at one end of the closed microchannel ( 2 ), - axial decoupling of transmitted light from the closed microchannel ( 2 ) at another end of the closed microchannel ( 2 ), - detection of the transmitted light in the light detector ( 11 ). Measurement method for a measuring device according to one of claims 11 to 13, comprising the steps: - supplying sample liquid ( 7 ) and preferably detection fluid ( 8th ) in the closed microchannel ( 2 ), - transversal irradiation of the closed microchannel ( 2 ) with light from the light source ( 4 ), which is preferably designed as an excitation light source, - axial coupling of light from the closed microchannel ( 2 ), - Detection of the decoupled light in the light detector ( 11 ).

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